JPH06200341A - Free cutting ti alloy with high rigidity - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a Ti alloy for machine parts that requires specific strength, high rigidity and machinability. [Composition] Al: 5.5-10%, B: 0.5-3.0%, O: 0.
25% or less, S: 0.01 to 1.0%, REM: 0.01 to 5.0%, balance Ti and inevitable impurities, and a free-cutting high-rigidity Ti alloy in which a metal boride is crystallized and / or precipitated. The Young's modulus improving element and the machinability improving element do not react with each other and coexist in the Ti alloy to provide high rigidity and free cutting property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to mechanical parts that are required to be lightweight and highly rigid, such as engine parts for automobiles (such as connecting rods, piston pins, cam shafts and crankshafts) and leg parts for aircraft. It is a high-rigidity Ti alloy suitable for use in high-rigidity Ti alloys with excellent machinability in order to mass-produce the aforementioned mechanical parts at low cost.
Regarding alloys.

[0002]

2. Description of the Related Art Ti alloys have extremely high specific strength as compared with steel materials, and at the same strength, the specific gravity is nearly 40% lighter. However, the Ti alloy has a problem that the machinability is extremely poor as compared with steel materials, and there is a problem that it becomes extremely expensive when processed into mechanical parts. Therefore, Ti alloys have only been applied to certain mechanical parts where the high cost can be tolerated to some extent.

In order to solve such a problem, for example, Japanese Patent Laid-Open No.
In JP-A 60-251239, S: 0.001 to 10% (hereinafter, "%" unless otherwise specified in this specification.
Means "% by weight"), REM: 0.005 ~
Free cutting Ti containing 10% and / or Ca: 0.001 to 10%
Alloys have been proposed. This proposal is for trace REM and
If one or both of Ca is added to the Ti alloy, S
It is said that the sulfide in the Ti alloy containing Ti becomes granular and the machinability is significantly improved without lowering the toughness and ductility.

[0004]

[Problems to be Solved by the Invention]
Furthermore, when S is added to the Ti alloy, the machinability of the Ti alloy is certainly improved. However, the characteristics of Ti alloy other than machinability,
Especially, the rigidity is not improved. Therefore, when the Ti alloy according to the above-mentioned proposal is applied to a mechanical component that requires rigidity, the rigidity is insufficient, and it is necessary to compensate for this insufficient rigidity by increasing the thickness of the mechanical component. As a result, the advantages of the alloy are impaired and the degree of freedom in designing mechanical parts is significantly impaired.

Therefore, the Ti alloy according to this proposal is
It cannot be applied to parts that require rigidity and machinability, such as connecting rods, piston pins, camshafts, crankshafts, and other automotive engine parts, aircraft leg parts, etc. I couldn't do that.

Here, an object of the present invention is a high-rigidity Ti alloy suitable for being applied to parts which are required to be lightweight and have high rigidity. In order to mass-produce the above mechanical parts at low cost,
Another object is to provide a free-cutting high-rigidity Ti alloy with improved machinability.

[0007]

Means for Solving the Problems By the way, the inventors of the present invention previously disclosed in Japanese Patent Application No. 4-212880 Al: 5.5-10%,
B: 0.5-3.0%, O: 0.07-0.25%, S as required
One or more of n, Zr and Hf: 20% or less, and / or V equivalent = V + (15/10) Mo + (15 / 6.3) Cr + (15 /
4.0) Fe + (15/36) Nb + (15/9) Ni + (15/25) One or more β-phase stabilizing elements that make W less than 15%, the balance Ti and inevitable impurities. We proposed a high-rigidity Ti alloy in which metal borides crystallize and / or precipitate in the alloy matrix.

To this high rigidity Ti alloy, Al and O are added in appropriate amounts to improve Young's modulus, and one or more of Sn, Zr and Hf are added to improve high temperature strength and creep resistance. By further adding a β-phase stabilizing element and dispersing titanium boride particles with a high Young's modulus in the matrix, hot working is possible and tensile strength: 90 kgf / mm ² or more, Young's modulus : We provide high-rigidity Ti alloys of 13000 kgf / mm ² or more.

By improving the machinability of the high-rigidity Ti alloy proposed by this Japanese Patent Application No. 4-212880, the present inventors can provide a free-cutting high-rigidity Ti alloy which can achieve the above object. As a result of further studies, we obtained the findings listed below.

Α phase stabilizing element (Al, O), if necessary, solid solution strengthening element (Sn, Hf, Zr) and β phase stabilizing element
Addition of S and REM to a Ti alloy containing (V, Mo, Cr, Fe, etc.) improves the machinability. Even if S and REM are added to the Ti alloy containing the solid solution strengthening element, the α phase stabilizing element, and the β phase stabilizing element, the rigidity is hardly reduced.

B is crystallized or precipitated in the matrix by forming hard dispersed particles of a compound with Ti (TiB), and the rigidity of the Ti alloy can be improved.
Even if REM is added, the morphology of crystallization or precipitation does not change, and hard dispersed particles of TiB are formed. Therefore, even if S and REM are added, the effect of improving rigidity by adding B can be maintained.

As described above, the addition of S and REM does not change the reaction of B in the Ti alloy.
The reaction in the Ti alloy does not change with the addition of B.
Therefore, by adding S 2 and REM to the Ti alloy containing B, the machinability can be improved while maintaining the rigidity. The present inventors have made further studies based on these findings and completed the present invention.

The gist of the present invention is as follows:
l: 5.5-10%, B: 0.5-3.0%, O: 0.25% or less,
S: 0.01-1.0%, REM: 0.01-5.0%, free-cutting high-rigidity Ti alloy characterized by having an alloy composition consisting of the balance Ti and unavoidable impurities and being formed by crystallizing and / or precipitating a metal boride. Is.

In the above-mentioned free-cutting high-rigidity Ti alloy according to the present invention, the high temperature strength is increased by containing 20% or less in total of one or more selected from the group consisting of Sn, Zr and Hf. be able to. In addition, at least one β-phase stabilizing element is represented by the following formula

[0015]

[Equation 2] V equivalent = V + (15/10) Mo + (15 / 6.3) Cr + (15/4) Fe ・ ・ ・ V content represented by In addition to improving the heat-treatability, it has the effect of suppressing the formation of Ti ₃ Al, so that more Al can be contained and the rigidity can be further improved.

[0016]

The operation of the present invention will be described in detail below. The present invention, as described above, Al: 5.5-10%, B: 0.5-3.
High rigidity Ti proposed by Japanese Patent Application No. 4-212880, in which 0%, O: 0.25% or less, the balance Ti and unavoidable impurities, and metal boride crystallizes and / or precipitates in the Ti alloy matrix. High-rigidity free-cutting with improved machinability by adding an appropriate amount of S and REM to the alloy
It is a Ti alloy.

All the essential additive elements and optional additive elements in the free-cutting high rigidity Ti alloy according to the present invention are roughly classified into (1) free-cutting expression component element and (2) high-rigidity expression component element (3) ) It becomes a high temperature strength developing component element and (4) high hot workability developing component element. Therefore, each is divided. In the free-cutting and high-rigidity Ti alloy according to the present invention, the free-cutting expression component element and the high-rigidity expression component element do not react with each other and independently improve the characteristics.

(1) Free Cutting Machinability Generating Element S: 0.01-1.0% S forms an inclusion to improve the machinability of the Ti alloy.
If the S content is less than 0.01%, inclusions are not formed in an amount sufficient to improve machinability, while if it exceeds 1.0%, the inclusions become coarse and some are formed along the grain boundaries, which results in heat treatment. Hot workability and fatigue strength decrease. Therefore, in the present invention, the S content is limited to 0.01% or more and 1.0% or less. Desirably 0.02
% Or more and 0.6% or less.

REM: 0.01 to 5.0% REM (rare earth element) such as La, Ce and Y is an element that easily bonds with S. By granulating the S compound, deterioration of ductility of the matrix is reduced. It is an element that suppresses the deterioration of hot workability and fatigue strength. If the REM content is less than 0.01%, the effect of reducing the deterioration of the ductility of the matrix is small, and it does not contribute to the suppression of the deterioration of hot workability and fatigue strength. On the other hand, if the REM content exceeds 5.0%, the viscosity of the Ti melt increases when it is mixed and melted in the Ti alloy, and segregation easily occurs. Therefore, in the present invention, the REM content is limited to 0.01% or more and 5.0% or less. Desirably, it is 0.05% or more and 4.0% or less. In addition,
The addition of REM is desirable because it can be inexpensively performed by using a commercially available Mm (Misch metal) containing La and Ce as the main components.

(2) High rigidity component element Al: 5.5-10% In the present invention, Al is an essential additive element. Al is an α-phase stabilizing element and significantly improves Young's modulus by solid solution hardening. The Young's modulus improving effect is not exhibited at a content of less than 5.5%, while when it exceeds 10%, Ti ₃ Al (α ₂
Phase) is produced in a large amount, which deteriorates both the ductility in both hot and cold. Therefore, in the present invention, the Al content is limited to 5.5% or more and 10% or less. Preferably 6.5
% To 8.5%.

B: 0.5 to 3.0% In the present invention, B is an essential additive element. B crystallizes and / or precipitates as titanium boride (TiB) during solidification and cooling, and has the effect of improving the Young's modulus of the Ti alloy. Since TiB has a Young's modulus of 50,000 kgf / mm ² or more, which is extremely high in Young's modulus as compared with Ti, when dispersed in a Ti alloy, it follows the compound rule of Ti alloy in proportion to the volume of particles in the Ti alloy. Young's modulus can be improved. When the B content is less than 0.5%, the amount of TiB crystallized and / or precipitated is small and the Young's modulus is not improved. On the other hand, if the B content exceeds 3.0%, the TiB dispersion amount increases, so that the Young's modulus improvement amount increases, but the ductility in both hot and cold regions remarkably decreases. Therefore, in the present invention, the B content is limited to 0.5% or more and 3.0% or less. Desirably, it is 0.7 to 2.0%.

According to the confirmation results of the present inventors, B
When the content is 1.0%, about 5% by volume of titanium boride is crystallized and / or precipitated and dispersed in the matrix, and B
When the content is 3.0%, about 15% by volume of titanium boride is dispersed.

According to the present invention, as will be described later, a neutral type element and / or a β-phase stabilizing element may be blended. In such a case, each additive element is solid-dissolved in the matrix. . However, most of Zr and Hf are solid-solved in the matrix, but crystallize and / or precipitate as a metal boride in a slight amount. The metal borides at that time are zirconium boride and hafnium boride.
However, due to the small amount and the Young's modulus of the boride itself is lower than that of titanium boride,
These do not contribute to the improvement of Young's modulus.

O: 0.25% or less In the present invention, O is an essential additive element and stabilizes the α-phase and improves Young's modulus like Al. It is not necessary to set the lower limit of the content because even if the amount is a small amount, such an effect is exhibited, but if the content exceeds 0.25%, the cold ductility of the Ti alloy is significantly reduced. Therefore, in the present invention, the O content is 0.25%.
Limited to: Desirably, the content is 0.1% or more and 0.2% or less.

In addition to Al and O, C and N are known as α-phase stabilizing elements, and these elements have Young's modulus improving effect like Al and O, but C is 0.3%. As described above, the addition of a trace amount of N of 0.1% or more significantly reduces the cold ductility of the Ti alloy. Therefore, in the present invention, it is desirable that neither C nor N be added. (3) High temperature strength developing component elements Sn, Zr, Hf: 20% or less of one kind or two or more kinds In the present invention, these elements are optional addition elements, and at least one kind is contained if necessary. A preferred combination is Sn and Zr (and / or Hf).
Sn, Zr, and Hf are all neutral type elements and have the effect of solid solution strengthening with respect to Ti alloys. Although the Young's modulus improvement effect is small, the high temperature strength can be increased and the application range of Ti alloy can be expanded. Therefore, it is desirable to add them in order to improve the properties of both high heat resistance and high Young's modulus. When the addition amount of these elements is small, the effect of deteriorating the ductility in both hot and cold is small and there is no problem. Become. Therefore, in the present invention, it is desirable that one or more of Sn, Zr, and Hf be 20% or less in total. More preferably, it is 1 to 12%.

These additional elements, which are neutral type elements, are mostly present in a solid solution form in the titanium alloy matrix according to the present invention. However, although Zr and Hf are small, some of them combine with boron and contribute to the formation of metal borides. In the case of Zr, its content is about 7/8 as a solid solution and about 1/8 contributes to the formation of metal borides. Similarly, in the case of Hf, it is considered that 3/4 forms a solid solution and about 1/4 contributes to metal boride formation.

(4) High hot workability-producing component element β-phase stabilizing element: V equivalent of 15% or less As the β-phase stabilizing element, for example, V, Mo, Cr, Fe, etc. are known. In the present invention, these β-phase stabilizing elements are optional additional elements, and at least one kind or two or more kinds are added as necessary. Although these β-phase stabilizing elements lower the Young's modulus, they have the effect of suppressing the formation of Ti ₃ Al, so that they can contain more Al, which has the Young's modulus improving effect in the present invention. Further, it also has the effect of improving the heat treatment property and decreasing the β transus (the temperature at which the β phase is transformed into the α + β phase) to improve the hot workability.

Of the β-phase stabilizing elements, V which is a solid solution type,
Mo has a large Young's modulus lowering effect, while eutectoid Cr and Fe have a smaller Young's modulus lowering effect. However, if any β-phase stabilizing element is added in such a large amount that it becomes a β-phase single phase, the Young's modulus significantly decreases, which is not preferable. Therefore, in the range where the Young's modulus is not extremely lowered, that is, in the total of at least one β-phase stabilizing element, the V equivalent by the above equation is 15
It is desirable to add in the range of not more than%. It is preferably 1 to 10%. In addition, the individual addition amount of each element corresponding to V equivalent: 15% is Mo: 10%, Cr: 6.3%, Fe: 4%
Is.

Compositions other than the above are Ti and inevitable impurities. In addition, there are N, H, etc. as unavoidable impurities,
For example, a total amount of 1% or less is acceptable. In particular, it is preferable to limit H: 0.05% or less and N: 0.1% or less for reasons of room temperature ductility.

The free-cutting high-rigidity Ti alloy according to the present invention having the above composition further improves its machinability while maintaining the high rigidity characteristic of the high-rigidity Ti alloy proposed in Japanese Patent Application No. 4-212880. Can be improved. Therefore,
It is a high-rigidity Ti alloy suitable for being applied to machine parts that are lightweight and require high rigidity, and since it has excellent machinability, the aforementioned machine parts can be mass-produced at low cost.

Next, a method for producing a free-cutting high rigidity Ti alloy according to the present invention will be described. Free cutting high rigidity Ti according to the present invention
The production of the alloy is not limited to a particular method as long as it is the same as that of the conventional Ti alloy. For example, known manufacturing methods of Ti alloy such as VAR method and arc melting method can be applied.

Specifically, Ti sponge which is a melting material,
Pure Al, electrolytic Sn, Zr sponge, pure Hf, Al-V mother alloy, and each of Cr, V and Mo, as well as Fe-S alloy as an S source, Al-S alloy, Ti-S alloy, REM After appropriately selecting Mm or the like as a source and blending it in a predetermined amount, and in order to crystallize / precipitate and disperse a metal boride for improving Young's modulus in a matrix, undissolved as a B source in the raw material. A low melting point Al boride (melting point 1720 ° C) and / or Fe boride (melting point 1650 ° C), which is unlikely to occur, is mixed and then alloyed as a melt by non-consumable electrode melting such as arc melting or VAR melting. Good. The amount of oxygen can be adjusted depending on the type of Ti sponge, but if a large amount is added, TiO ₂ may be used.

When TiB ₂ is used as the B source, the melting point is 32.
Since it is 25 ℃, it is not melted by VAR melting, and there is a problem in melting such as side arc generation. Further, even when the non-consumable electrode is melted, TiB ₂ may be undissolved, and a good quality ingot in which crystallized substances and / or precipitates of metal borides are dispersed cannot be obtained. Further, since B alone has a melting point of 2100 ° C., the same problem may occur. Therefore, when using these, it is necessary to use a melting method having higher energy such as electron beam melting.

Therefore, by using at least Al boride and / or Fe boride as a raw material for melting the B source, the metal boride is uniformly crystallized and / or precipitated in the matrix after solidification and cooling after melting. . Since the dispersed particles are almost equal to the density of the matrix (about 4.5), segregation etc. does not occur and they are extremely uniformly dispersed. further,
Since such metal borides are dispersed particles that have been crystallized and / or precipitated, the generated particles are extremely stable, and even when heat treatment such as hot working or heat treatment is performed, the reaction between the matrix and the metal boride occurs. It does not form a layer and does not deteriorate the mechanical properties of the Ti alloy.

The Ti alloy ingot thus produced is hot-worked at a temperature of 1000 to 1200 ° C., forged,
It can be a rolled material. Furthermore, it is possible to adjust the mechanical properties to desired values by heat treatment such as annealing.
Further, the present invention will be described in detail with reference to examples, but this is an example of the present invention and the present invention is not limited thereto.

[0036]

EXAMPLES Alloys having the compositions shown in Tables 1-1 and 1-2 (Examples of the present invention: No. 1 to No. 21, comparative examples: No. 22 to No. 3)
0, Conventional example: No. 31 to No. 36, free-cutting Ti alloy, industrial pure Ti or Ti alloy) Each was melted in a skull melting furnace to form an ingot with a diameter of 60 mm and a length of 100 mm.

After subjecting these ingots to homogenization treatment of 1150 ° C. × 8 hrs → air cooling, they were reheated to 1150 ° C.,
A bar with a diameter of 20 mm and a length of about 300 mm and 20 mm x 60 mm x about 300 m
Forged with m plate material. In Table 1-3, the cracks observed during the hot forging are indicated by "x" in the hot workability column.

Then, after solution treatment of 800 ° C. × 1 hr → air cooling, tensile test pieces (parallel part diameter 6 mm, gauge length 30 mm), hot upsetting test pieces (diameter 8 mm, length 12 mm) , Young's modulus measurement test piece and drilling test piece (20 mm × 50
(mm × 250 mm), each of which is subjected to a test to obtain tensile strength (normal temperature) and elongation (normal temperature and 700
℃), Young's modulus and machinability were measured, and hot workability was evaluated.

(Young's modulus) It was measured by the resonance method. (Machinability) It was evaluated by a drill drilling test. The conditions are shown below. Drill material: Carbide (K20 equivalent) Drill diameter: 6 mm Feed: 0.1 mm / rev. Rotation speed: 980 rpm Lubrication: Water-soluble lubricant, 41 / min. Hole depth: 15 mm (non-penetrating hole) Table 1- The machinability shown in 3 was calculated by the following formula based on the perforation possible distance in pure Ti. Here, the permissible drilling distance is the product of the number of holes drilled by the life of the drill and the depth of the holes.

[0040]

[Equation 3]

(Hot workability) Evaluation was carried out by performing compression tests of 70% and 85% at a strain rate of 1 S ^-1 at 800 ° C. using an upsetting test piece, and in Table 1-3, 70% Those with no cracks by compression are shown as "○", and those without cracks with 85% compression are shown as "◎".

[0042]

[Table 1-1]

[0043]

[Table 1-2]

[0044]

[Table 1-3]

In the example of the present invention, Young's modulus target value: 13500 kgf
/ mm ² is exceeded and the conventional examples (No. 31 to No. 36) are greatly exceeded, ensuring high rigidity. The machinability (drillability) was about 100%, which was not much different from the conventional example (free-cutting Ti alloy), and the machinability was also greatly improved.

On the other hand, No. 22 had an Al content below the lower limit of the range of the present invention, so that the Young's modulus was insufficient.
In No. 23, the Al content was above the upper limit of the range of the present invention, so the hot workability was poor.

In No. 24, the B content was below the lower limit of the range of the present invention, so the Young's modulus was insufficient. No.25 is
Since the B content exceeds the upper limit of the range of the present invention, the hot workability is deteriorated.

In No. 26, the O content exceeded the upper limit of the range of the present invention, so the ductility at room temperature decreased. N
In o.27, the total amount of Sn, Zr, and Hf exceeded the upper limit of the range of the present invention, so the hot workability was deteriorated.

In No. 28, since the content of the β-phase stabilizing element exceeds the upper limit of the range of the present invention, the Young's modulus was lowered. In No. 29, the S content exceeded the upper limit of the range of the present invention, so the hot workability was deteriorated.

In No. 30, since the S content exceeded the upper limit of the range of the present invention and the REM content exceeded the upper limit of the range of the present invention, the Young's modulus decreased. No.31 is the conventional Ti-6Al-4V-based free-cutting Ti alloy (No.1), and No.32 is the conventional Ti-6Al-4V-based free-cutting Ti alloy.
(No. 2), No. 33 is a conventional Ti-3Al-2.5V-based free-cutting Ti alloy, and No. 34 is a conventional pure Ti-based free-cutting Ti alloy.
Alloy, No.35 is pure Ti for industrial use, and No.36
Is a conventional Ti-6Al-4V, but it can be seen that the Young's modulus is insufficient in each case.

[0051]

As described in detail above, according to the present invention,
For example, it is possible to provide a Ti alloy for machine parts such as connecting rods, piston pins, cam shafts, crankshafts, and other automobile engine parts, aircraft leg parts, and the like, which require specific strength, high rigidity, and machinability.

Claims (3)

[Claims] 1. By weight%, Al: 5.5-10%, B: 0.5-
3.0%, O: 0.25% or less, S: 0.01 to 1.0%, REM: 0.
A free-cutting high-rigidity Ti alloy characterized by having an alloy composition of 01 to 5.0%, the balance being Ti and unavoidable impurities, and being formed by crystallizing and / or precipitating a metal boride. 2. The alloy composition further comprises Sn, Zr and Hf.
20 in total of one or more selected from the group consisting of
The free-cutting high-rigidity Ti alloy according to claim 1, characterized in that the content is less than or equal to wt%. 3. The free-cutting high-rigidity Ti according to claim 1 or 2, further comprising at least one β-phase stabilizing element in a V equivalent represented by the following formula in an amount of 15% by weight or less. alloy. [Equation 1] V equivalent = V + (15/10) Mo + (15 / 6.3) Cr + (15/4) Fe